This application claims the priority of Austrian patent document 2 A A 1360/2004, filed Aug. 10, 2004, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a power branching transmission for motor vehicles having an internal-combustion engine which drives an input shaft of the power branching transmission, which power branching transmission has several branches comprising at least one power shift transmission with a number of gears and has an output shaft.
A hydromechanical transmission is known from U.S. Patent Document U.S. Pat. No. 3,979,972, which is constructed in the manner of a power branching transmission and comprises an input shaft connected with an internal-combustion engine and an output shaft. In this case, clutches and planetary transmissions are provided in a first branch between the input shaft and the output shaft; whereas a hydrostatic drive operates in a second branch, which hydrostatic drive is in an operative connection with spur gears and has two pump motors situated behind one another.
German Patent Document DE 199 54 894 A1 to a power branching transmission which is suitable for tractors, wheel- and chain-driven machine tools and utility motor vehicles. The power branching transmission has a mechanical branch, a hydrostatic branch and one or more planetary transmissions by way of which the mechanical power fraction and the hydrostatic power fraction are combined again.
German Patent Document DE 101 28 853 A1 (corresponding U.S. Patent Publication No. US2005/157583) discloses a motor vehicle which has a transmission line with a drive unit, a transmission and a clutch device for the transmission of torques between the drive unit and the transmission. The clutch device is constructed as a multiple clutch device, particularly as a double clutch device, with a first clutch arrangement assigned to a first transmission input shaft and a second clutch arrangement assigned to a second transmission input shaft.
According to German Patent Document DE 101 28 853 A1, a transmission line with an internal-combustion engine is installed into a motor vehicle, which internal-combustion engine interacts with a double clutch transmission or a power shift transmission. Between the internal-combustion engine and the projecting transmission, a double clutch is provided from which an input shaft extends to the above-mentioned transmission. An output shaft driving the wheels of a rear axle is provided on a countershaft of the transmission.
It is an object of the invention to provide a highly effective power shift transmission for motor vehicles which offers multiple application possibilities and is distinguished by a simple transmission construction.
According to certain preferred embodiments of the invention, this object is achieved by providing a power branching transmission for motor vehicles having an internal combustion engine driven transmission input shaft, said power branching transmission comprising a plurality of transmission branches including a power shift transmission with a plurality of gears and an output shaft, wherein at least one of the branches is equipped with a control device operable to change rotational directions of the output shaft during starting operation of the motor vehicle, and wherein the control device is operable to continuously influence the rotational speed of the output shaft with shifted gears of the power shaft transmission connected with the input shaft.
This object is further achieved by providing a method of operating a power branching transmission for motor vehicles, having an internal-combustion engine which drives an input shaft of the power branching transmission, which power branching transmission has several branches comprising at least one power shift transmission with a number of gears and has an output shaft wherein at least one of the branches controls the power branching transmission in such a manner that, during the starting operation of the motor vehicle, the rotating direction of the output shaft can be changed, and during the starting operation and with the shifted gears of the power shift transmission connected with the input shaft, the rotational speed of the output shaft can be continuously influenced.
Important advantages achieved by means of the invention are that a continuously operating, easily producible power branching transmission is conceived which operates with a change of the transmission ratio, which does not interrupt the tractive power, from a maximal speed when reversing to the maximal speed when driving forward, in which case a start from a stopped condition is permitted. In this case, a precise positioning and maneuvering of the motor vehicle is ensured by the control drive, preferably the hydrostatic device. The size of the hydrostatic device can also primarily be determined by the required tractive powers and the permissible differential pressure of the hydrostatic device. As a result of the ratios in the compound planetary transmission, it becomes possible to keep the displacement volume in the fixed-displacement motor of the hydrostatic device relatively low. Furthermore, a perfect transmission efficiency is achieved, specifically by low hydrostatic power fractions, particularly at higher gears and higher speeds. In addition, required transmission spreads can be achieved with an arbitrary number of mechanical gear ratio positions. Finally, a retarder function can also be implemented in connection with the hydrostatic device. Furthermore, the power branching transmission is suitable for machine tools—tractors, construction machines, handling vehicles, telehandlers, stackers—and vehicles for the stop-and-go operation—city buses, feeding vehicles, street cleansing vehicles. Finally, the above-mentioned transmission can be used in passenger cars and utility vehicles, where special demands are made with respect to driving and operating comfort.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.